The invention concerns a two-stage high-power semiconductor laser, including a medium-power laser, in the form of a two-dimensional array, which pumps a "lasing" material constituting a high-power laser. The structure according to the invention is different from known structures in that the two stages are not separate and facing each other, as in existing devices, but interpenetrate each other, either in hybrid or integrated form.
Solid semiconductor lasers, made from group III-IV materials such as GaAs, AlGaAs, GalnP, etc. are well known but, whether they are made of discrete parts or in the form of bars integrating several elementary lasers, they provide only small amounts of energy compared with gas or excimer lasers, for example, which are used for industrial applications requiring high power, such as cutting of ceramics, metals or cloth, or in medical applications.
The low power of elementary lasers--or even rods of lasers--has led to their combination into integrated circuit arrays including several rods of lasers on a substrate, the rods alternating with reflecting bars angled at 45.degree.. The result is that these integrated laser circuits emit a light beam at 90.degree. to the main surface of the substrate. Such an integrated laser circuit is described in the French patent n.degree.2 639 150 filed on 15 Nov. 1988 by the applicant. The structure is summarized in FIG. 1 in which only the parts necessary to understand the structure are included and described. A substrate 1 of semiconducting materials carries several parallel rods such as 2 and 3 in which are formed a plurality of elementary lasers 4, using techniques known to professionals of the art. The longitudinal faces of the rods 2 and 3 perpendicular to the plane of the substrate 1 are located so as to form Fabry-Perrot cavities, such that the laser strips 4 emit, via the two cleaved faces, a light beam in a plane parallel to the main surface of the substrate. Reflecting bars are located between the rods 2 and 3 and parallel to them; their sides are rounded or inclined at 45.degree. and reflect the light emitted by the lasers perpendicularly to the main surface of the substrate.
Emissive arrays applying this concept have been made: their dimensions are about 1 cm; by grouping several hundred or thousand elementary lasers of 100 .mu.m size an optical power of 1 kW can be achieved.
To increase the peak power even more and improve the spectral purity, one known technique is to associate a solid laser and at least one emissive integrated laser array of the type described above, which supplies the optical pumping energy for the solid laser.
A solid laser, as opposed to a semiconductor laser (which is also solid), is one in which bars of square or round section, about 5 cm by 5 mm, or arrays of material such as the YAG (yttrium-aluminum-garnet), YLF (yttrium-lithium-fluorine) or LiNbO.sub.3 (lithium niobate), doped with neodymium for example. These bars emit coherent light in the windows centered on 1.06, 1.55 or 2.1 .mu.m, respectively, when they are excited. There are many publications on this subject, since optical pumping by semiconductor lasers gives a significantly better yield than pumping by a flash lamp (limited to about 1%).
FIG. 2 shows the association of a solid YAG laser, for example, and an optical pumping device making use of semiconductor lasers. The main faces of a YAG array 6 are sandwiched between at least two emissive laser arrays 7 and 8 whose emitted beams are oriented towards the array 6 which produces a secondary emission. This type of association is known, for example, in the patent by the applicant previously mentioned and the patent U.S. Pat. No. 5,115,445, dated 19 May 1992. FIG. 2 should be interpreted widely, since there are known examples of solid lasers 6 pumped by a plurality of elementary semiconductor lasers or in rods whose light energy is directed towards the solid laser 6 by means of a system of mirrors or optical fibers.
Whatever the geometrical form of the association shown in FIG. 2 between:
one or more semiconductor lasers, PA1 illuminating, either directly or by reflection via flat or conical reflectors or optical fibers or lenses or any other combination of these, PA1 one or more solid lasers in the form of cylindrical bars or arrays, PA1 a second stage constituted by at least one solid laser of a material pumpable by the light energy emitted by said primary lasers which excite this secondary laser;
all the associations have one common characteristic: the optical pumping lasers are geometrically or spatially separated and do not form an integrated structure. These associations of primary and secondary lasers may form a single device by using mechanical means of attachment, yet the materials of the semiconductor lasers and the solid laser (YAG) do not interpenetrate in a single layer.